Pyrazolo pyrazines, 3-amino

An efficient one-pot synthesis of some novel azolo[l,5-a]pyrimidines, via enaminonitriles, has been described <00SC1985>. The utility of 3-aminocinnamonitrile in the synthesis of new pyrazolo[l,5-a]pyrimidines has been reported <00ZN(B)321>. The synthesis of novel arylaminopyrazolo[3,4-d]pyrimidin-4-ones has been described <99IJC(B)1075>. The synthesis and properties of a-Thiagra, a substituted 5-(2-thienyl)pyrazolo[4,3-d]pyrimidin-7-one bioisostere of Viagra, have been described <00H(53)2643>. Imidazo[4,5-b]pyrazines are obtained by the reaction of 4-amino- 5-imino-imidazole derivatives with acetophenone dimethylacetal . 

The syntheses of some pyrazolo[l,5-a]pyrazines from A-amino-pyrazinium derivatives have been described.345 Treatment of 266 R R2 = H or Me) with base gave 267, which cyclized to 268 with EP or DMAD. The A-imino derivative (270), from the interesting A-amino-pyrazinium A -oxide salt (269) gave 41 % of 271 with EP.345... 

Af-Acetoxy-3-amino-2-pyrazinecarboxamidine (190) gave 3-(5-methyl-l,2,4-oxadiazol-3-yl)-2-pyrazinamine (191) (AcOH, reflux, 90 min 72%) that underwent isomerization to 3-acetamido-1 //-pyrazolo[3,4-/ ]pyrazine (192) (EtONa, Me2NCHO, reflux, 1 h 60%).1115... 

Pyrazin-l-oxid 2-Amino-3-cyan-5-methyl- E9b/2, 283 [HO-N = CH-CO-CH3 + NC-CH(NH2)-CN] lH- ... 

Only two reports have been found dealing with the chemistry of this ring system. In the first of these the amination of several simple pyrazine derivatives such as the dimethyl compound (1) with hydroxylamine O-sulfonic acid to give the corresponding iV-amino compounds is described. Treatment of the latter with derivatives of acetylenecarboxylic acid provides pyrazolo[l,5-a]pyrazines such as 2 in 2-10% yields. In contrast, the N-oxide of 1 gave a 41% yield of the 5-oxide 3. Condensation of the... 

Base-sugar condensations have been used to prepare 2 -deoxyribosides of pyrazin-2-ones,30.31 3,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines,32 and indazoles, where about equal amounts of 1- and 2-glycosylated products were obtained, although with P-selectivity.33 Reaction of 2-deoxy 3,5-di-O-toluoyl-a-D-cryt/iro-pentofuranosyl chloride with 2-amino-6-chloropurine under Seela s phase-transfer conditions gives the p-A. giy osylated product as the major isomer.34... 

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